Just trying to understand the reason why my radiator top hose keeps changing shape. It starts out flat (collapsed) and if I start the engine and then open the coolant filler cap it just regains its shape straight away!


I have no problem with changing it out but I want to know why it happens. Is it just that the hose is old or is there some kind of vacuum or air lock I need to attend to. No point installing a new hose if it is just going to do the same thing.


Thanks to any mechanical engineers out there that can tell me the reason why it does this.


Cheers
Alan

id bleed your system...Still persists perhaps your thermostat

When the coolant gets up to temperature, the water vapour that forms above the water-based coolant forces out the atmosphere gases that are in there when it's cold if the pressure exceeds the value on the pressure cap. When the engine cools down the water vapour returns to water, and there is normally a one-way vent on the pressure cap that allows atmospheric pressure back in to replace the water vapour. However if the atmosphere cannot flow back in, a vacuum will be created, thus the hose collapses under external pressure of the atmosphere.

Sounds like a problem with the pressure cap, not with the hose itself.

Thank you, that sounds like it makes sense!
Alan